The present invention relates to a process for the preparation of compounds containing hydroxyl groups from polyurethane urea or polyurea waste products and their use in the production of polyurethane resins.
It is known that synthetic resins produced by the polyisocyanate polyaddition process, in particular foams, can be broken up into low molecular weight components by suitable reactive solvents and converted into a soluble form. One of these methods is alcoholysis, in particular glycolysis, in which polyhydric alcohols, in particular glycols, are used to decompose polyisocyanate polyaddition products and dissolve the products of decomposition. Publications describing such processes include: DE 1,110,405; DE 2,238,109; DE 2,304,444; DE 2,414,091; DE 2,516,863; DE 2,557,172; DE 2,738,572; DE 2,759,054; DE 2,902,509; DE 3,702,495; U.S. Pat. No. 3,109,824; 3,404,103; 3,632,530; 3,983,087; 3,738,946; 3,632,530; 3,300,417; 2,937,151; 4,014,809; 4,110,266; 4,159,972; 4,162,995; EP 11,661 and EP 105,167.
EP-A-11,661 discloses a process for decomposing flexible polyurethane foams, according to which a relatively high molecular weight, non-distillable polyhydroxyl compound is incorporated with the reaction mixture after glycolysis. At least part of the glycol still present is then removed by distillation.
The above-listed publications do not, however, provide a solution to the problem of decomposition of polyurethane urea or polyurea waste products by alcoholysis to recover useful products. Nor do these disclosures address the particular problem of working up synthetic resins produced from polyisocyanate mixtures of the diphenylmethane series and aromatic diamine chain lengthening agents.
Only DE-PS 4,024,601 deals with the problem of converting polyisocyanate polyaddition products prepared by the RIM process to useful starting materials. According to this disclosure, the reaction with low molecular weight polyhydric alcohols is carried out with a ratio by weight of synthetic resin to alcohol of at least 3:1 and is followed by mixing of the products of alcoholysis with so-called primary polyols to form stable dispersions of high viscosity.
The high viscosity of the products of the process of DE-PS 4,024,601 is a disadvantage which makes it difficult to use high proportions of the products of alcoholysis for reprocessing by the polyisocyanate polyaddition process. Reprocessing which makes it possible to almost completely reuse the scrap synthetic resin would, of course, be desirable. Attempts to reduce the viscosity of the end product of the alcoholysis by employing higher reaction temperatures and/or longer reaction times for alcoholysis resulted in the reaction product containing an undesirably high proportion of diamines corresponding to the diisocyanates which had been incorporated into the scrap resin.